1. Field of the Invention
The present invention relates to a signal cancellation method and a signal cancellation device. More specifically, a method and device for signal cancellation wherein a portion of an input signal is split, the phase and amplitude components thereof are adjusted so as to have the opposite phase as a split signal, and wherein by recombining these, the input signal is cancelled.
A signal cancellation device (circuit) is presently widely used in signal cancellation loops which are used in such equipment as self-adjusting feed-forward amplifiers. Specifically, in a feed-forward amplifier, by combining a distortion extraction loop, which amplifies an input signal and cancels the input signal component from said signal, and a distortion cancellation loop, which cancels the distortion signal component generated by the amplifier, an amplified signal in which the distortion component is suppressed can be ultimately obtained.
2. Description of the Prior Art
FIG. 15 is a block diagram of a conventional input signal cancellation loop. In the figure, the input signal cancellation loop of FIG. 15 includes a conventional cancellation loop circuit 10, a splitter 11, which splits a given of the input IN into 2 signals A and B (where the ratio is optional), a delay line 12, which delays signal A by the same time as the processing system for signal B, a cancellation adjuster 60, which adjusts the phase and amplitude of the signal B, a phase adjuster 61 and an amplitude adjuster 62 (attenuator, etc.) thereof, an amplifier 14, which amplifies signal B after the aforesaid phase adjustment, and a combiner 13, which combines the delayed signal A′ of the delay line 12 and the cancellation signal B′ after amplification.
Furthermore, the input signal cancellation loop of FIG. 15 has an automatic controller 50, which monitors the combined signal C of the output OUT and performs automatic control of the cancellation adjuster 60 so that the amplitude of said signal C is within a specified level (≈0), a wave detector 52, which performs wave detection on the amplitude of the composite signal (extracted signal) C of the output, an A/D converter (A/D) 53, which performs A/D conversion on the wave detection output, a CPU 54, which incorporates a control program for cancellation adjustment, which is described hereinunder, D/A converters (D/A) 55, 56, which performs D/A conversion on the amplitude control signal CA and phase control signal CP, respectively, and a common bus 57 of the CPU 54.
To summarize the operation, a given signal of the input IN is split into the 2 signals A and B by the splitter 11, one signal A is delayed by the delay line 12 to become a delay signal A′. The other signal B is adjusted in phase and amplitude by the cancellation adjuster 60, then amplified by the amplifier 14, and becomes cancellation signal B′ for canceling the delay signal A′. Additionally, the 2 signals of A′ and B′ are combined by a combiner 13, and become the composite signal C of the output OUT.
Meanwhile, in this state the automatic controller 50, along with monitoring the amplitude of the composite signal C, alternately controls the phase adjuster 61 and amplitude adjuster 62 in respective time division so that said amplitude becomes 0, and by this means the cancellation signal B′ is adjusted to the opposite phase and same amplitude as the delay signal A′, thus canceling the input signal. The conventional signal cancellation method is explained in detail below in accordance with a vector diagram.
FIGS. 16 (a) through 16 (f) show a diagram explaining a conventional input signal cancellation method. When the initial status at a certain point in the circuit is represented as (a), the cases where adjustment is performed first from the phase (b) and (c) and cases where adjustment is performed first from the amplitude (d), (e), and (f) are respectively indicated in time sequence. In the initial status of the FIG. 16 (a), signal B can assume various phases and amplitudes with respect to the vector (hereinafter the vector is referred to as a signal) A′ that is the object of cancellation, but by adjusting this signal B so that it becomes a cancellation signal B′ (having the opposite phase and the same amplitude as signal A′), the input signal can be canceled.
When starting adjustment from the phase, the process advances from the figure (a) to the figure (b). In the FIG. 16 (b), when the phase of the signal B is rotated in the direction of the arrow b, the output signal C when the opposite phase as the signal A′ becomes minimal. In the FIG. 16 (c), when the amplitude of the signal B is reduced in the direction of the arrow c, the output signal C when the amplitude is the same as that of the signal A′ becomes minimal (C=0). Thus, when starting adjustment from phase, typically, adjustment is completed in the 2 steps of the figures (b) and (c).
On the other hand, when starting adjustment from amplitude, the process advances from the figure (a) to the FIG. 16 (d). In the FIG. 16 (d), when the amplitude of the signal B is reduced in the direction of the arrow d, the output signal C becomes minimal and at the point intersecting the circle r. In other words, the head of the output signal C, which is the composite signal of the 2 signals A′ and B, in accordance with a reduction in the amplitude of the signal B, moves downward on the segment L1, which is parallel to the signal B, as indicated by the broken line in the figure, but when the output signal C and segment L1 become orthogonal, the amplitude of the output signal C becomes minimal.
It should be noted that, when the output signal C moves toward the head of signal B′ at this time, signal C becomes orthogonal to signal B, and accordingly a right triangle is formed having the signals B′, C and B as its sides. The circle r is a circle which has signal B′ as a radius and is externally tangential to the right triangle, and accordingly the relation whereby the output signal C is minimized at the point at which the aforesaid reduction (or increase) in signal B and the circle r intersect is always established so long as signal B and the circle r intersect.
In the FIG. 16 (e), when the phase of the signal B is turned in the direction of the arrow e, the output signal C when in the opposite phase as the signal A′ becomes minimal. In the FIG. 16 (f), when the amplitude of the signal B is increased in the direction of the arrow f, the output signal C when the same amplitude as signal A′ becomes minimal (C=0). Thus, when starting adjustment from amplitude, typically, adjustment is completed in the 3 steps of the figures (d)˜(f).
FIGS. 17 A and 17 B show a diagram explaining the range of control by a conventional system, wherein FIG. 17 (A) shows the range of control by vector expression. In FIG. 17 (A), by combining signal B with signal A′, which is the object of cancellation, the composite signal C of the output is formed, and the purpose of control is to make this composite signal C=0.
The physically changeable range of the phase and amplitude are determined by the circuit configurations (settings) of the respective phase adjuster 61 and amplitude adjuster 62. Here, the interior of the region W1, which satisfies both, becomes the physically controllable range. It should be noted that the circle r, as explained in the aforesaid FIG. 16 (d), is composed of the aggregation of points at which the composite signal C becomes minimal in the control of amplitude of signal B, and the amplitude control of the signal B must intersect with the circle r until the signal B reaches its minimal value within the physically controllable range (indicated by the circle R2). Accordingly, the actual (practical) control range becomes the region W2, which is narrower than the physical control range W1.
FIG. 17 (B) represents the control range of FIG. 17 (A) in the form of a graph (orthogonal plane), and the physical control region W1 and practical control region W2 are respectively shown in correspondence with FIG. 17 (A). As explained in reference of FIGS. 16 (b) and 16 (c), when starting from phase adjustment, by means of the phase control shown in FIG. 16 (b), the phase differential between the signals A′ and B can be adjusted to 180 degrees (indicated in the figure by the arrow p), so that, in the amplitude control shown in the following FIG. 16 (c), the signal A′ is effectively canceled.
However, as explained in reference of FIGS. 16 (d)˜(f), when beginning from amplitude adjustment, if signal B happens to be in the region W2 (indicated by the arrow a in the figure) the minimal value of the composite signal C can be detected in amplitude control, and accordingly the next phase control can be performed normally, but if it is between W1 and W2, before the minimal value of the composite signal C can be detected, the physical control range R2 of the amplitude adjuster 62 is exceeded, and the minimal value of the composite signal C can no longer be detected. Thus, an obstacle to the control algorithm for automatic control, which is described below, is created.
In this connection, it is possible to set the physical control range R2 of the amplitude adjuster 62 so as to be smaller. By this means, as shown in the aforesaid FIG. 16 (d), even if the signal B is in the phase Bi, it is still possible barely to detect the minimal point of the composite signal C. The detection of this minimal point, in terms of FIG. 17 (B), corresponds to detection in the arrow b.
However, if signal B after amplitude adjustment thereby becomes too small, in the phase adjustment in the following FIG. 16 (e), the change in the composite signal C will be sluggish (small), even if the phase of the small signal B is rotated, thus creating impediments to the detection control and detection precision of the minimal point phase in the automatic controller 50. Moreover, in the amplitude control of the following FIG. 16 (e), it is necessary to return the amplitude of the signal B to a larger size, and while this type of hunting adjustment is performed as described above, a composite signal C having a large amplitude will be output to the output OUT.
To give an extreme example, if the amplitude adjuster 62 provided is that so that the physical control range can be up to R2=0, in FIG. 16 (d), for example, even in the initial phase in which the signal B does not intersect with the circle r, although adjustment is possible to a point such that signal B=0, as a result, the minimal point of the composite signal C cannot be found in the phase control of FIG. 16 (e), and accordingly, an obstacle to the control algorithm for automatic control is created.
FIGS. 18 (A) and 18 (B) show a flowchart for the conventional automatic control process. FIG. 18 (A) depicts an example of an automatic control process, where input is made to this process when the circuit power is switched on. In step S11, initial setting of the phase adjuster 61 and amplitude adjuster 62 is performed in accordance with the default parameters. In step S12, it is determined whether the output signal amplitude C>TH (specified threshold value). If C>TH, then the amplitude C of the output signal exceeds the permitted range, so after an alarm signal is output in step S17, the process advances to step S13. If C is not greater than TH, then the process advances directly to step S13.
In step S13, the phase control signal CP is changed slightly in one direction. In step S14, it is determined whether or not the minimal point of the output signal C has been detected, and if the minimal point has not been detected, the sequence returns to step S13. When the output signal C has ceased decreasing and begins to increase during the process of the continued repetition of steps S13 and S14, then the minimal point has been detected, and otherwise, there has been no minimal point detection. In this case, when the output signal C increases after the initial change of the aforesaid phase adjustment signal CP, the direction of the change of the phase adjustment signal CP is reversed.
When in due course there had been minimal point detection according to the discrimination in the aforesaid step S14, in step S15, the amplitude control signal CA is slightly changed in one direction. In step S16, it is determined whether there has been minimal point detection of the output signal C, and if there is no minimal point detection, the sequence returns to step S15. When minimal point detection occurs in due course, the sequence returns to step S12. The processes of the aforesaid steps S12 and S17 may be provided so as to follow the aforesaid step S16.
FIG. 18 (B) shows another example of automatic control processing, where, instead of the above-described minimal point detection of the output signal C, a specified number (such as approximately 1 time to 5 times) of continuous decreases is detected. The same step numbers are used for steps which correspond to those in the process shown in FIG. 18 (A), and the explanation thereof is omitted. In step S18 of this process, it is determined whether a specified number of decreases in the output signal C have been detected, and if there has been no such detection, the sequence returns to step S13. If the output signal C in the repeated series of steps S13 and S18 begins to increase after decreasing, then the process skips step S18 to the Yes side. If the output signal C increases from the initial change in the phase adjustment signal CP, then the direction of change of the phase adjustment signal CP is reversed. Similarly, in step S19, it is determined whether the specified number of decreases in the output signal C has been detected, and if not detected, the sequence returns to step S15. Then, when in due course the specified number of decreases has been detected, the sequence returns to step S12.
As described above, a conventional signal cancellation loop alternately adjusts the phase and amplitude of the cancellation signal B by the phase adjuster 61 and amplitude adjuster 62.
However, when starting from the amplitude adjustment, since the minimal point of the signal B for minimizing the output signal C changes to a greater extent than the phase difference between the two signals A′ and B, first, unless the control of amplitude is started from the minimal point of the phase, it takes time to find the optimal point, and, in the worst cases, the control range for amplitude is violated. For this reason, it is necessary to start the cancellation process from phase.
Moreover, even if control is started from phase, in actuality there are many cases where a disturbance (such as fluctuations in phase) occurs at the time of shifting to amplitude control, and when a disturbance occurs in this timing, ultimately the control route described in reference of FIGS. 16 (d)˜(f) must be followed, and the automatic control of signal cancellation becomes unstable.
Heretofore, in cases where the signal A′ which is the object of cancellation is used as a standard, when the phase P of the signal B falls outside of the range of −90°≦P≦90°, since a minimal point does not exist during amplitude control, the practically controllable range has been greatly restricted. Moreover, if the condition of signal B amplitude≈0 were permitted, since the minimal point of the following phase cannot be detected, the automatic control for signal cancellation would become unstable.